Controlling strength gain and permeability using slag cement

Abstract

In bridge decks, low permeability and high durability are desired concrete properties. These properties are often achieved by using concrete with a low water to cementitious material ratio (w/cm), incorporating supplementary cementitious materials (SCMs), or a combination of both. Reducing the w/cm and including SCMs also increases concrete compressive strength, which is not necessarily a desired property for bridge decks. Researchers have observed less cracking in bridge decks containing concrete with compressive strengths less than 40 MPa. Developing a concrete with low permeability and a compressive strength less than approximately 40 MPa can be challenging. This paper documents the development and performance of a concrete mixture that had a specified maximum compressive strength at 56 days of age of 42 MPa and was classified as having low permeability. Several variables were examined in the research project, which included SCM type and content, binder content and w/cm. One mixture contained 50% slag cement and a total cementitious material of 307 kg/m3 met the specifications. This mixture was then used to cast a bridge deck that has been in service for approximately 5 years and exhibits a minimal amount of cracking when compared to bridge decks of approximately the same age.